Non-catalytic NO. reduction triple in a coaxial tube burner for that we have proposed for waste liquid incineration was investigated using urea solution atomized under various conditions. Because the temperature in the riser does not exceed the optimum range for NO reduction under the experimental conditions, NO emission decreases as temperature in the riser at the position of urea atomization increases. Also, the presence of water has little effect on NO reduction under the experimental conditions. Therefore, NO reduction behavior can be correlated to the normalized stoichiometric ratio. The correlation was also experimentally confirmed.